Free cutting alloy



Patented Jan. 8. 1935 1,986,826

UNITED STATES PATENT OFFICE mun CUTTING Annoy Howard L. Hopldns, Cleveland, Ohio, assignor to Aluminum Company of America, Pittsburgh, Pas, a corporation of Pennsylvania No Drawing. Application September 18, 1933,

, Serial No. 689,890

' The invention relates to aluminum basealloys 1.5 per cent of bismuth or of bismuth and cadand is particularly concerned with such alloys mium. For 'the purpose of my invention the elecontaining copper, manganese and silicon. ments bismuth and cadmium are substantially An extensively used alloy of this nature contains equivalent when used together in the same alloy by 5 from about 3.0 per cent to about 5.5 per cent of reason .of the similarity in eflect on the machining 5 copper, from about 0.25 per cent to about. 1.5 per h eri tics of the all ycent of manganese, and from about 0.25 per cent Ihave found that bismuth is an alloying conto about 2.0 percent of silicon, the balance being stituent which has avery favorable effect upon the commercial aluminum. This alloy can be memachining properties of aluminum base alloys. chanically deformed by the well known commer- Bismuth in conjunction with cadmiumlikewise 1o cial processes such as rolling, forgin drawing, or, has a beneficial influence on the machinability of extrusion. The grain is thereby refined and the aluminum alloys of the kind herein described. physical properties considerably improved and In this sp ifl i il i the pp d laim I suitable thermal treatments have been devised to use the term free machining" when applied to 18 enhance the improvement. The alloy has been these constituents to indicate this advantageous used for many applications among which may be effect on the machining properties, as evidenced mentioned airplane propellers and connecting by the fact that the alloys containing bismuth or rods for internal combustion engines. 'bismuth and cadmium withinthe disclosed range Thereare, however, some applications wherein may be machined more rapidly, with less tool M the alloy might be conveniently and profitably wear, less tool sharpening, better quality of chip 20; used were it not for an inherent disadvantage and a smoother machined surface than similar which militates against its'use in these-applicaalloys not containing these elements. j A tions. Mechanical cutting operations such as Although improvement in machinability of the drilling, shaping, or lathe-cutting are su essdisclosed aluminum base alloys may be effected ,2 fully carried out only by using certain precautions by the addition of from about 0.05 to 1.5 per cent which increase the cost of production and perof bismuth, I prefer to employ between about 0.25 haps favor the choice of another alloy which can and 1.2 per cent of this element. A preferred combe machined more readily but-which is in other position which exemplifies the physical properties respects, r instance in phy ical properties. not of the basealloy and the aforesaid improved mar so desirable. when alloys are diflicult tomachine chining characteristics is an alloy containing this disadvantage becomes evident in many cases a ut 4,4 p r cent of copper. 0.8 per cent o mailthrough rapid wear of the cutting tool edge which anese, 0.8 per c n of SilicOn and 1 P cent of necessitates frequent .1- l I such bismuth, the balance being substantially all alucases where machining is diilicult, continual lubrimi -1m I cation is required, the machined surface is rough The simultaneous presence of bismuth and cadand irregular, and the chip has a tendency to form mm in the base alloy pp to be m r v continuous curls or spirals that may foul the tool tageous in certain cases than the same total or the operating parts of the machine. The deamount of bismuth. For example, the addition sirability. is immediately apparent of an alloy of of about 0.5 per cent of bismuth and 0.5 per cent (0 good working characteristics, and of cadmium simultaneously produces a more dis-. 40

physical properties, yet M 1 favorable tinct improvementinthe machining quality of an -machining qualities that finish machining aluminum base alloy containing about 4.4 per operations may be performed economically, succent oi copper, 0.8 per cent of manganwe, and 0.8

cessfully, and may be productive of a pleasing per cent of silicon, balance substantially alumidd surface appearance. num, than the tion of about 1 per cent of L Accordingly, an object of the invention is-the bismuth. The total amount of bismuth and cadproduction of an aluminum base alloy containing mium may vary between about 0.05 and 1.5 per from about 3.0 per cent to about 5.5 percent of cent although I prefer to use a total of from about copper, from about 0.25 per cent to about 1.5 per 0.25 to 1.2 per cent of these two elements. .By cent of manganese and from about 0.25 per cent 'virtue of the superior machining quality obtained 50 to about 2.0 per cent 'of silicon which may bethrough use of both bismuth and cadmium, it is readily and economically subjected to cutting possible to attain a given degree of machinability operations. I with a smaller amount of added elements than if My invention resides in the discovery that this bismuth is used alone. This feature is of particu- 5| object is effected by the addition of from 0.05 to lar advantage where a restriction exists on the total amount of elements than can be present in the alloy other than those contributing to the strength or ductility of the alloy.

The tensile properties of the aluminum-coppermanganese-silicon alloys are not materially affected by the presence of bismuth. However; if cadmium is also present, there is a tendency for an increase in strength, yield point and Brinell hardness with'a corresponding decrease in elongation depending on the amount employed. Through this effect of cadmium it is possible not. only to improve the machining quality of the base i alloy, but to increase the strength. A further advantage ofour discovery lies in the fact that an alloy of high strength and hardness may be readily machineda result not heretofore obtained in the so-called heat treated strong I aluminum alloys.

Thebismuth may be most conveniently added to themolten aluminum alloy in solid metallic form since it melts at a temperature considerably below that of aluminum or its alloys. If more than about 1.5 per cent of the element is to be'added cadmium is added to the alloy, the temperature at thetime of making'the addition and subsequent thereto should not exceed about 1400' F.

to avoid excessive volatilization of the element.

The term aluminum" used herein and in the appended claims embraces the usual impurities found in aluminum ingot of commercial grade or picked up in the course of the usual handling operations incident to ordinary melting practice.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those skilled in the'art for the purpose of improving or. altering their physical characteristics.

Iclaim:f-- I Y. 1. An aluminum base alloy consisting of from about 3 to 5.5 per 'cent of copper, from about 0.25 to 1.5 per cent of manganese, from about'0.25 to 2 per cent of silicon, and from about 0.05 to 1.5 per cent of bismuth, the balance being aluminum.

2. An aluminum base alloy consisting of from about 3 to 5.5 per cent of copper, from. about 0.25

.to 1.5 per cent of manganese,-from about 0.25 to 2 per cent'of silicon, and from about 0.25 to 1.2 per 'cent of bismuth, the balance. being aluminum.

3. .An aluminum base alloy containing about 4.4 per cent of copper, about 0.8 per cent of'manganese, about 0.8 per cent of silicon, and about 1 percent of bismuth, the balance being aluminum Howard: L. nor xms. 

